The invention relates generally to the field of welding filler metals, and more particularly to compositions suitable for welding aluminum alloys.
Many different processes are known and currently in use for joining metal articles, including brazing and welding. Both such operations may be used for joining of aluminum and aluminum alloy articles. Unlike steels and other metals, aluminum alloys present unique problems owing, for example, to their metallurgy, their melting points, the changes in strength as a function of particular alloying agents, and so forth. Moreover, increasing interest in both thinner aluminum alloy workpieces on one hand, and thicker workpieces on the other presents additional difficulties in the selection of brazing and welding materials that perform well and provide the desired physical and mechanical properties.
Brazing operations use a filler metal with a melting temperature that is lower than the base metal being joined. In brazing, the base metal is not melted and the alloying elements in the filler metal are selected for their ability to lower the melting temperature of the filler metal and to wet the aluminum oxide always present on the base metal so that a metallurgical bond can be achieved without melting the base metal. In some applications, brazing may be conducted in a furnace under vacuum or protective atmosphere where the temperature is raised until only the filler metal melts and fills the joint between the solid base metal members through fluid flow and capillary action. Brazed joints are commonly used for low strength aluminum alloys, and for very thin section structures, such as radiators for automobiles, and for heat exchangers such as those used in heating, ventilation and air conditioning systems. The temperatures used in brazing may anneal both non-heat treatable and heat treatable aluminum alloys, which may alter the mechanical properties achieved either by cold working or heat treatment and aging operations. Therefore, brazing, while quite useful in many applications, may not be suitable to join high strength structural alloys.
Welding operations join metal parts by melting a portion of the base metal of each work piece to be joined, as well as by melting of the filler metal to create a molten weld pool at the joint. Welding requires concentrated heat at the joint to create the molten weld pool which upon solidification has a resultant chemical composition that is a combination of the chemistries of the filler metal and the base metal. Welding temperatures may often be controlled to be sufficiently high to melt both the filler metal and the base metal, but also to keep the heat affected zone of the base metal to a minimum in order to retain its mechanical properties.
The adder materials, both for brazing and welding, are typically delivered in the form of wire, which, depending upon the application, may be in the form of continuous lengths that are fed though a welding torch, or in shorter lengths that may be hand-fed, or even as rods, such as flux-coated rods for stick welding. Currently available aluminum alloy brazing and welding wires do not, however, satisfy the needs of many modern applications. For example, current products do not offer the desired fluidity during the joining operation, or the desired strength when combined with base material in welding applications, particularly when used with a range of modern welding processes. Moreover, where welding arcs vary in penetration, heat, weld pool formation, and so forth, current aluminum alloy wires and compositions do not provide a desired degree of consistency in terms of the composition and strength of the ultimate joint.
There is currently a need for improved aluminum alloy compositions that are suitable for welding (and brazing) applications that successfully address such needs.